The world of High Voltage technology lacks coherent, universal standards for the various High Voltage equipment used. As a result, there is a relatively large variety of national standards from country to country presently a real challenge to High Voltage equipment manufacturers. This is especially so in the field of High Voltage tap-changing equipment.
Tap-changers used, for example, to change the tap settings on a commercial transformer, utilize input signals for control and monitoring. Known tap-changers utilize electromechanical contacts for control.
A user typically connects their equipment (e.g. transformer) to the tap-changer motor drive. Digital signals are an effective means to control and monitor the functioning of the tap-changer. In the digital world, a “1” and a “0” describe a status of full voltage (On) or zero voltage (Off). In High Voltage applications, these two statuses are typically described by, for example: AC of 50-60 Hz, 110-240V±15% of rated voltage, or DC of 24-48V±10% of rated voltage. In the traditional motor drive, this is a user choice, where the motor drive must be equipped with a special apparatus to interface with a particular voltage for switching of the electromechanical contacts. Accordingly, a different apparatus is required to be used for different voltage levels.
Each of the above-mentioned voltage levels and configurations is individually relatively easy to design for, but not the total combination of variations. For example, the problem may be described as follows: actuation (of the tap-changer) should only occur upon the receipt of a valid signal, however, with such a large range of valid signal levels as described above, a disturbance signal for 220VAC very likely will be a valid signal level, for example, for other voltage schemes. Therefore, accurate signal recognition is an important issue.
In addition, if a digital input (DI) is constructed to function for relatively low voltage levels and consumes several mA of current (at the relatively low voltage levels), it will correspondingly dissipate a relatively large amount of energy for higher voltages. Moreover, usually the DI must be isolated and protected for over-voltage. At times, the system may be required to consume a relatively large amount of current for a relatively short period of time. This is especially so for a DI that is energy economical. The higher current contributes to the burning of oxides on the digital output (DO) in the case that it is a relay.
Still further, the signals must be converted to a suitable digital signal with relatively high resolution.
In addition, traditional control systems utilize electromechanical contacts, which are limited in the voltage levels that may be applied thereto, but are also disadvantageously subject to mechanical wear and tear.
Therefore, what is desired then, is a system and method for accurately handling all of the common voltage variations commonly encountered within a switchyard with the same equipment for a tap-changer.
It is further desired to provide a system and method that reduces and/or eliminates the use of electromechanical contacts for control of the tap-changer.
It is still further desired to provide a system and method that provides a flexible approach to monitoring and diagnostics of a tap-changer, even from a remote location.